The ether start uses the same switch the flame heater used. In order to test, find the coolant temperature sensor for the ether start. It usually sits on the flange for the upper coolant hose and has a connector with two contacts. Pull the connector, short the contacts with a paper clip. Preferably with the ether bottle off, you can now flick the switch and should hear an audible "click" of the solenoid that sits where the neck of the ther bottle screws into.
The ether start will deliver a very small amount of ether, whenever the switch is activated AND the coolant is below a certain temperature, regardless of whether the engine is turning or not. Therefore follow the advice on the warning sign and only operate the ether start with the engine cranking to make sure the fumes are somewhat equally distributed between the cylinders.